Protecting Coastal Waters

Florida Keys wastewater district is satisfying its mission to improve local water quality.

Protecting Coastal Waters

Plant Operations and Facilities Manager Ryan Dempsey (left) and Field Operations Manager Mike Dempsey of the Key Largo Wastewater Treatment District inspect some of the newer sewage pumps at a facility in Key Largo. (Photography by Steven Martine)

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To many people, the Florida Keys are paradise, the subject of Hemingway novels and love songs. But to those responsible for maintaining the environmental sustainability of their thriving waters, every day is a fine balancing act.

When the Key Largo Wastewater Treatment District was created in 2005 to change private septic systems to a public collections system, the intent was to prevent further degradation of waters surrounding the 16-mile-long island. The district is meeting its objective, but the vacuum collections system required by such high-water-table areas is much more complex and high maintenance than standard gravity flow systems. The nearly constant threat of power outages, flooding and fires caused by hurricanes creates an ongoing challenge to keep the system operating at peak efficiency.

“In 2002, the state of Florida designated the Florida Keys an Area of Special Concern,” explains Nick Rodriguez, chairman of the Key Largo Wastewater Treatment District Board of Commissioners. “This led to an unfunded mandate from Tallahassee, requiring Monroe County and the Florida Keys to develop, plan and implement advanced wastewater treatment processes.”

With nearly every home on the island being waterfront property, this mandate was for the protection of nearshore waters and canals, into which aging septic tanks were leaking. It resulted in the formation of the district, and a vacuum sewage collections system started going into the ground in 2006. Only the laterals running from homes and businesses into the vacuum main are standard gravity flow pipes.

“Due to the coral rock, the hard ground we have, and the water table, we could not install a conventional gravity sewer system,” says Ryan Dempsey, plant operations and facilities manager. “We had to go with a vacuum system.

“We went with Airvac out of Rochester, Indiana, for our vacuum collections system: pits, station control panels, pump skids.”

Challenges spur innovation

To maintain this extensive system, the district has 22 service trucks, a backhoe loader, a skid steer, two Vac-Tron (now Vermeer MV Solutions Inc.) vacuum trailers, two portable generators for emergency lift station power and a gas pump for repairs.

They’re also in the process of developing a mobile vacuum trailer. The district’s need to contend with hurricanes and their attendant floods and even sometimes fires that break out in the wake of storms led them to seek out a rolling vac station.

“We have seven vac stations,” Ryan Dempsey says. “Eventually, we will be able to pull this trailer up to any of them, pipe in, run wire over for power and controls, and essentially get that station up within a few hours in the event of a major fire, flooding, hurricane, what have you.”

The area recently suffered indirect effects from Hurricane Ian, which caused almost 3 feet of standing water to spill into the streets. Residents were being asked to refrain from any more toilet-flushing than absolutely necessary, due to strain on the wastewater system.

Before that, the last major storm was Hurricane Irma in 2017. The district’s 3.45 mgd sequential batch reactor treatment plant was purposely built on a high area about 300 yards off the beachfront to avoid flooding.

“We didn’t sustain any intrusion in our buildings or equipment, but our infrastructure out in the collections system did get a lot of water due to storm surge and flooding,” Ryan Dempsey says. “We also lost power at our main plant and all of our vacuum stations. One of our biggest challenges with Hurricane Irma was the recovery of the vacuum system. A lot of downed trees and debris made it very difficult for us to access our vacuum pits and valves to isolate and recover the system.”

The district learned from that event and got through it fairly well.

“We had our system up within five days after the hurricane,” recalls Michael Dempsey, field operations manager. This was important, because residents of The Keys are always under mandatory evacuation during hurricanes and are not permitted to return until all critical services are restored.

Preventive maintenance

For obvious reasons, the district must always be prepared for emergencies. The preventive maintenance program entails daily maintenance on seven vacuum stations — each of which has five vacuum pumps and two or three sewage pumps — and timing of the vacuum pits and buffer tanks, which is performed quarterly.

“That keeps the collections system efficient and optimized, as far as the vacuum energy required to retrieve the wastewater,” explains Ryan Dempsey.

Maintenance crews use a GIS system and BS&A’s Cloud-Based Utilities Management Suite to manage work orders and daily inspection scheduling. “Customer calls get logged and dispatched through that software, and it helps us keep track of historical events,” Rodriguez says. “It gives us an idea of our trouble areas, so we can harden those to prevent future issues.”

New monitoring system

Determined to stay out in front of problems, tighten up the collections system and reduce callouts, the district has contracted with Flovac Americas to install a radio-telemetry wireless monitoring system. This state-of-the-art monitoring system, partially funded through a grant from the U.S. Army Corps of Engineers, will help prevent sanitary sewer overflows and warn operators of potential issues.

“The vacuum system is very complex,” Ryan Dempsey explains. “There are a lot of moving parts out in the field, compared to a conventional gravity wastewater system. Each vacuum pit has a vacuum valve and a controller, which have a lot of very small parts and components that can fail. That’s the nature of the system and why we are required to stay on top of our timing and inspections of our vacuum pits. That prompted us to want this monitoring system, to catch abnormalities in the vacuum pits and buffer tanks before they become bigger issues.”

Given the location, you might expect that infiltration and inflow was a major issue driving implementation of the telemetry monitoring, but Ryan Dempsey says the bigger factor was notification of vacuum leaks and hung valves that would have otherwise taken far more time and effort to track down. “In the rare event that we do have I&I, it will also trigger this system because that requires more vacuum energy and our whole system is run on vacuum.”

Efficiency is critical, so when the district encountered challenges with the pumps that deliver wastewater from the vacuum tanks into the force main, they turned to United Flow to engineer a better solution.

“A lot of our vacuum components will start to fail slowly, start to hang open longer during each event,” Ryan Dempsey says. “This system is designed to have counters, floats and switches that monitor all that. If anything falls outside the setpoints, it’ll alarm us before it becomes an emergency event. What we’re hoping is that we’re able to attend to these issues before they are emergencies, or call-in the middle of the night, or on holidays or weekends.”

Ideally, this will extend the system longevity, and save on electrical costs and labor, moving forward.


The district also recently installed the largest solar project in Monroe County. It’s another totally grant-funded enterprise, putting solar panels at every vacuum station in the plant, and in the administration office. Six of their seven vacuum stations in the collections system are now solar-powered, along with nine in-office solar arrays, and seven arrays at the wastewater treatment plant, including a covered parking area.

“Our storm retention area is completely covered by solar, and one of our first projects was to cover our chlorine contact chamber with solar,” says Ryan Dempsey. “We had ideas just to limit the UV exposure for our chlorine usage, to help optimize our chlorine usage in our disinfection chamber. But it was a kill-two-birds-with-one-stone situation because we minimized chlorine costs as well.”

The project is now at substantial completion. All of the arrays are currently producing power and the district should see a return on its $2.6 million investment within about 20 years. Other than occasional rinsing of debris, the solar panels are essentially maintenance-free.

“We’re hoping to cover about 25% of our electricity costs with this solar project,” Rodriguez notes.

Lean and green

In this way, the district is also taking steps toward greener operations.

“We find ourselves stewards of the environment,” says Rodriguez. “The whole reason we have our wastewater district is to care for our delicate ecosystem here in The Keys. That’s why we were funded, so anything we can do to continue following that, including solar and renewable energy, is something we take seriously and pursue.”

Along those lines, the district is currently looking at a pre-equalization tank to optimize and level out batches going into its sequencing batch reactor tanks. It will optimize the whole process and help manage the amount of flow coming into each tank at any given period.

“Currently, we have low-flow periods, due to nighttime and (other situations), where we’ll have really low tanks, and then the morning tanks will be much higher,” Ryan Dempsey says. “It’s difficult to set up our aeration, chemical feed and waste scheduling with those changing tank levels. The pre-equalization tank will really help optimize all of that.”

The other situations he speaks of include weekend peaks and high flows during special tourist events like mini-lobster season. “Mini-season is the weekend before official lobster fishing season starts. Noncommercial, recreational-only fishermen get first shot at the lobsters. Our population swells to three times what it normally is for that weekend.”

To combat exposing their system to such extremes, district staff depend on experience. “We’ve been doing it for years and we just know what we need to do ahead of time,” says Michael Dempsey. “We don’t really know how many people are going to come down, we just know we’re going to be overwhelmed, and we prepare for that.”

The district has historical data from high-flow weekends and operators know how the plant has reacted to specific settings, what the numbers looked like and what the biology looked like.

“We use that information to make an educated assessment of what we need to do as far as our settings, air times and plant set-up, and it really helps,” Ryan Dempsey says. “That pre-eq tank will help us optimize those settings even further.”

Significant improvements

All these individual efforts are gradually moving the district to where it wants to be, environmentally and cost-wise. The telemetry monitoring from Flovac  is estimated to be fully implemented within five to seven years, starting with the basins that are currently most problematic. The cost on that system is $7.5 million.

“We were originally about $89 million into debt to construct the system and the plant,” reports Rodriguez. “Since that time, we are just under $10 million in debt. Nearshore water quality has scientifically been proven to have improved since the inception of the system, and since protecting our nearshore waters was the whole reason for our construction, it’s one of our biggest successes.”

They’ve seen significant improvement in the quality aquatic life in the reefs, along with the canal system throughout Key Largo, as well.

“I’m especially proud of our solar system. To be the largest producer of solar electricity in Monroe County is no small feat for our little utility district. I think it speaks to our mission to preserve and protect the Florida Keys.”


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